VISCOSITY

STREAMLINE AND TURBULENT FLOW

               In a fluid each particle follows exactly same path and same velocity as its predecessor.Then the flow is said to be  steady or laminar or streamline. streamline flow is maintained only so long as the velocity of the fluid is below a certain limiting value is called the critical velocity.When the velocity exceeds this critical value,the flow becomes irregular ZIG-ZAG or turbulant.

                                   VISCOSITY

                consider the streamline flow of liquid over a horizontal fixed surface the different layer parallel to the surface will have different velocities.The top most layer has maximum velocity.

                                            Consider two adjacent layers separated by distance dx having the velocities v and (v+dv).The upper layer moves faster than lower one .The upper layer experiences a force dragging it backwards similar to the force of friction which opposes relative displacement between two solid surfaces.In this case of fluids such a force is called internal friction or force of viscosity.

 

Link: http://www.way2science.com/viscosity/